Device having multiple switching buffers for data paths controlled based on IO configuration modes

ABSTRACT

A device includes a first data terminal, a second data terminal, a first switching buffer coupled between a data node and the first data terminal and a second switching buffer coupled between the data node and the second data terminal. The first switching buffer and the second switching buffer are arranged such that a distance between the first switching buffer and the second data terminal is shorter than a distance between the second switching buffer and the second data terminal and that a distance between the first switching buffer and the first data terminal is shorter than a distance between the second switching buffer and the first data terminal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/645,124, filed Mar. 11, 2015, which claims the filing benefit ofJapanese patent application No. 2014-054342 filed on Mar. 18, 2014.These applications are incorporated by reference herein in theirentirety and for all purposes.

BACKGROUND

Field of the Invention

This invention relates to a semiconductor device, in particular, asemiconductor device that has a plurality of memory cell arrays.

Description of the Related Art

In a semiconductor device, such as DRAM (Dynamic Random Access Memory),a memory cell array is divided into multiple regions and datainput/output terminals, data buses, etc., are arranged between thedivided memory cell array regions in many cases (see patent document 1).

-   -   [Patent document 1] Japanese Laid-Open Patent Publication No.        8-139287

However, some methods of assigning memory cell array regions and databuses and of laying out data buses pose various problems, such as ashift in data input/output timing between memory cell array regions, anincrease in the number of necessary shield lines, and a change in datainput/output timing depending on operation modes.

In one embodiment, there is provided a device that includes a memorycell array including a plurality of memory cells, a data node coupled totransfer data from/to a selected one of the plurality of memory cells, afirst data terminal, a second data terminal, a first switching buffercoupled between the data node and the first data terminal and a secondswitching buffer coupled between the data node and the second dataterminal. The first switching buffer and the second switching buffer arearranged such that a distance between the first switching buffer and thesecond data terminal is shorter than a distance between the secondswitching buffer and the second data terminal and that a distancebetween the first switching buffer and the first data terminal isshorter than a distance between the second switching buffer and thefirst data terminal.

In another embodiment, there is provided a device that includes anactive area having a square shape divided into first, second, third,fourth, fifth, sixth, seventh, eighth and ninth regions arranged in amatrix, a plurality of memory arrays each including a plurality ofmemory cells arranged in each of the first, second, third and fourthregions, a plurality of data terminals arranged in the eighth region, afirst switching buffer coupled between a data node of one of the memoryarrays and one of the data terminals, a second switching buffer coupledbetween the data node of the one of the memory cell arrays and adifferent one of the data terminals. The first, second, third and fourthregions are arranged at respective corners of the square. The fifthregion is arranged at a center of the matrix. The sixth, seventh, eighthand ninth regions are arranged between the first and second regions, thesecond and third regions, the third and fourth regions and the fourthand first regions, respectively. The first switching buffer is arrangedin the seventh region. The second switching buffer is arranged in theseventh region.

In still another embodiment, there is provided a device that includes afirst memory array, a second memory array, a plurality of first dataterminals and second data terminals arranged in the first directionbetween the first memory array and the second memory array, a thirdmemory array arranged such that the first memory array is arrangedbetween the third memory array and the plurality of first data terminalsand second data terminals, a fourth memory array arranged such that thesecond memory array is arranged between the fourth memory array and theplurality of first data terminals and second data terminals and a databus. The data bus is configured to couple each of the first memory arrayand the second memory array to the first data terminals in a firstoperation mode, couple each of the first memory array and the secondmemory array to the second data terminals in a second operation mode,and couple to the third memory array and the fourth memory array to thesecond data terminals in each of the first operation mode and the secondoperation mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an overall configuration of a semiconductordevice according to an embodiment of the present invention;

FIG. 2 is a plan view of a layout of a prototype of the semiconductordevice;

FIG. 3 is a diagrammatical view for explaining the structure of a databus DB in the prototype;

FIG. 4 is a timing chart for explaining the operation timing of thesemiconductor device having a prototype-based layout, including FIG.4(A) depicting, transfer of read data read out of a memory bank BANK0and FIG. 4(B) depicting transfer of read data read out of a memory bankBANK2;

FIG. 5 is a plan view of a layout of the semiconductor device accordingto a first embodiment, showing a case where a first operation mode isselected;

FIG. 6 is a plan view of a layout of the semiconductor device accordingto the first embodiment, showing a case where a second operation mode isselected;

FIG. 7 is a plan view showing a configuration of one memory cell arrayARY according to an embodiment of the invention;

FIG. 8 is a circuit diagram of a buffer BF1L according to an embodimentof the invention;

FIG. 9 is a circuit diagram of buffers BF2L, BF2U, and BF4 according toan embodiment of an invention;

FIG. 10 is a timing chart for explaining operation timing according tothe first embodiment, including FIG. 10(A) depicting transfer of readdata from the memory bank BANK0 in the first operation mode and FIG.10(B) depicting transfer of read data from the memory bank BANK2 in thefirst operation mode;

FIG. 11 is a plan view of a layout of the semiconductor device accordingto a second embodiment, showing a case where the first operation mode isselected;

FIG. 12 is a plan view of a layout of the semiconductor device accordingto the second embodiment, showing a case where the second operation modeis selected;

FIG. 13 is a diagram for explaining the structure of the data bus DB,including FIG. 13(A) depicting the structure of a data bus DB0La, FIG.13(B) depicting the structures of data buses DB0Ub and DB1La, FIG. 13(C)depicting the structures of data buses DB1U and DB2L, and FIG. 13(D)depicting the structure of a data bus DB2U;

FIG. 14 is a first timing chart for explaining a read operation timingaccording to the second embodiment;

FIG. 15 is a second timing chart for explaining a write operation timingaccording to the second embodiment;

FIG. 16 is a third timing chart for explaining a shield structure in theread operation according to the second embodiment;

FIG. 17 is a plan view of a first modification of the layout of thesemiconductor device according to the second embodiment, showing a casewhere the first operation mode is selected; and

FIG. 18 is a plan view of a second modification of the layout of thesemiconductor device according to the second embodiment, showing a casewhere the first operation mode is selected.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an overall configuration of a semiconductordevice according to an embodiment of the present invention.

The semiconductor device 10 of this embodiment is a DDR 4 (Double DataRate 4) DRAM packaged in a single semiconductor chip, and is mounted onan external substrate 2. The external substrate 2 is a memory modulesubstrate or mother board, and includes a reference resistance RZQ. Thereference resistance RZQ is coupled to a calibration terminal ZQ of thesemiconductor device 10, and the impedance of the reference resistanceRZQ is used as reference impedance to a calibration circuit 30. Thereference resistance RZQ is supplied with a ground voltage VSS in thisembodiment.

As shown in FIG. 1, the semiconductor device 10 includes eight memorybanks BANK0 to BANK7. Each of the memory banks BANK0 to BANK7 is capableof operating exclusively, that is, capable of independently executing acommand, and has a memory cell array 11, a row decoder 12, a columndecoder 13, and a main amplifier MAMP. The memory cell array 11 hasmultiple word lines WL, multiple bit lines BL and /BL, and memory cellsMC arranged at the intersections of the word lines WL and the bit linesBL and /BL. A word line WL is selected by the row decoder 12, while abit line BL is selected by the column decoder 13.

Paired bit lines BL and /BL are coupled to a sense amplifier SAMPdisposed in the memory cell array 11. The sense amplifier SAMP amplifiesa potential difference created between the bit line BL and the bit line/BL and supplies read data obtained by amplifying the potentialdifference to a complementary local IO line LIOT/LIOB. The read datasupplied to the local IO line LIOT/LIOB is transferred to acomplementary main IO line MIOT/MIOB via a switch circuit TG. The readdata on the main IO line MIOT/MIOB is then converted into a single-endedsignal by the main amplifier MAMP, and is supplied to a datainput/output circuit 39 via a data bus DB.

The semiconductor device 10 also includes an address terminal 21, acommand terminal 22, a clock terminal 23, power terminals 24 and 25, adata input/output (IO) terminal DQ, and the calibration terminal ZQ,which serve as external terminals.

The address terminal 21 is a terminal that receives an address signalADD and a bank address signal BADD that are incoming external signals.The address signal ADD and bank address signal BADD input to the addressterminal 21 are supplied to an address control circuit 32 via an addressinput circuit 31. The bank address signal BADD supplied to the addresscontrol circuit 32 is used as a signal for selecting any one of thememory banks BANK0 to BANK7. An address signal ADD representing a rowaddress XADD is supplied to the row decoder 12 of a selected memorybank, and an address signal ADD representing a column address YADD issupplied to the column decoder 13 of a selected memory bank.

The command terminal 22 is a terminal that receives an incoming externalcommand signal COM. The command signal COM input to the command terminal22 is supplied to a command decoder 34 via a command input circuit 33.The command decoder 34 is a circuit that generates various internalcommands by decoding the command signal COM. Internal commands includean active signal ACT, a read signal READ, a write signal WRITE, and acalibration signal ZQC.

The active signal ACT is a signal that is activated when the commandsignal COM indicates a row-accessing command (active command). When theactive signal ACT is activated, the row address XADD supplied to theaddress control circuit 32 is supplied to the row decoder 12 of aselected memory bank. As a result, a word line included in the memorycell array 11 of the selected memory bank is selected based on the rowaddress XADD.

The read signal READ and the write signal WRITE are activated when thecommand signals COM indicate a read command and a write command,respectively. When the read signal READ or Write signal WRITE isactivated, the column address YADD supplied to the address controlcircuit 32 is supplied to the column decoder 13 of a selected memorybank. As a result, a bit line BL or /BL included in the memory cellarray 11 of the selected memory bank is selected based on the columnaddress YADD.

When the active command and read command are input and the row addressXADD and column address YADD are also input in synchronization withinput of the active command and read command, therefore, read data isread from the memory cell MC specified by the row address XADD andcolumn address YADD. The read data is transferred to the datainput/output terminal DQ via the main amplifier MAMP and the datainput/output circuit 39, and is output from the data input/outputterminal DQ to an external element.

When the active command and write command are input, and the row addressXADD and column address YADD are also input in synchronization withinput of the active command and write command, and then write data isinput to the data input/output terminal DQ, the write data is suppliedto the memory cell array 11 via the data input/output circuit 39 and themain amplifier MAMP and is written to the memory cell MC specified bythe, row address XADD and column address YADD.

The calibration signal ZQC is a signal that is activated When thecommand signal COM indicates a calibration command. When the calibrationsignal ZQC is activated, the calibration circuit 30 executes acalibration operation, thereby generates an impedance code ZQCODE.

The external terminals included in the semiconductor device 10 will bedescribed again. The clock terminal 23 receives incoming external clocksignals CK and /CK. The external clock signal CK and the external clocksignal /CK are complementary to each other, and are supplied to a clockinput circuit 35. Receiving the incoming external clock signals CK and/CK, the clock input circuit 35 generates an internal clock signal PCLK,which is supplied to a first internal clock generator 36. The firstinternal clock generator 36 generates a phase-controlled internal clocksignal LCLK based on the internal clock signal PCLK. The first internalclock generator 36 may be, for example, a DLL circuit. Circuits otherthan a DLL circuit may be used as the first internal clock generator 36.The internal clock signal LCLK is supplied to the data input/outputcircuit 39, which uses the internal clock signal LCLK as a timing signalfor determining timing of outputting read data.

The internal clock signal PCLK is supplied also to a timing generator37, which generates various internal clock signals ICLK based on theinternal clock signal PCLK. The internal clock signals ICLK generated bythe timing generator 37 are supplied to such circuit blocks as the rowdecoder 12 and column decoder 13, where the internal clock signals ICLKregulate the operation timing of the circuit blocks.

The power terminal 24 is a terminal supplied with the source voltagesVDD and VSS. The source voltages VDD and VSS supplied to the powerterminal 24 are supplied to an internal voltage generator 38, whichgenerates various internal voltages VPP, VOD, VARY, and VPERI and areference voltage ZQVREF, based on the source voltages VDD and VSS. Theinternal voltage VPP is a voltage used mainly by the row decoder 12, theinternal voltages VOD and VARY are voltages used by the sense amplifierSAMP in the memory cell array 11, and the internal voltage VPERI is avoltage used by a number of other circuit blocks. The reference voltageZQVREF is a reference voltage used by the calibration circuit 30.

The power terminal 25 is a terminal supplied with source voltages VDDQand VSSQ. The source voltages VDDQ and VSSQ supplied to the powerterminal 25 are supplied to the data input/output circuit 39. The sourcevoltages VDDQ and VSSQ are identical in potential with the sourcevoltages VDD and VSS supplied to the power terminal 24, respectively. Toprevent power noise generated by the data input/output circuit 39 frompropagating to other circuit blocks, the source voltages VDDQ and VSSQare used exclusively as source voltages to the data input/output circuit39.

The calibration terminal ZQ is coupled to the calibration circuit 30.When activated by the calibration signal ZQC, the calibration circuit 30carries out the calibration operation, referring to the impedance of thereference resistance RZQ and to the reference voltage ZQRVEF. Theimpedance code ZQCODE acquired by the calibration operation is suppliedto the data input/output circuit 39, where the impedance of an outputunit included in the data input/output circuit 39 is specified accordingto the impedance code ZQCODE.

A layout of the semiconductor device 10 will then be described.

Before description of layouts according to embodiments of the presentinvention, a prototype-based layout will first be described.

FIG. 2 is a plan view of a layout of a prototype of the semiconductordevice 10.

According to the layout of the prototype of FIG. 2, memory cell arrays11 comprising 8 memory banks are divided into 32 memory cell arrayregions ARY0 to ARY31 arranged into 4 columns of memory cell arrayregions in the X direction and into 8 rows of memory cell array regionsin the Y direction. Each row of 4 memory cell array regions comprisesone memory bank. For example, 4 memory cell array regions ARY0 to ARY3make up the memory bank BANK0.

Memory cell array regions ARY0 to ARY15 comprising memory banks BANK0 toBANK3 are arranged closer to one edge L1 (upper edge) of the chip in theY direction, while memory cell array regions ARY16 to ARY31 making upmemory banks BANK4 to BANK7 are arranged closer to the other edge L2(lower edge) of the chip in the V direction. A region formed between thememory cell array regions ARY0 to ARY15 and the memory cell arrayregions ARY16 to ARY31 is used as a peripheral circuit region PE0extending through the central area of the chip in the X direction.

External terminals, such as the address terminal 21, command terminal22, and data input/output terminal DQ, are placed in the peripheralcircuit region PE0 such that the address terminal 21 and commandterminal 22 are placed closer to one edge L3 (left edge) of the chip inthe X direction while the data input/output (IO) terminal DQ is placedcloser to the other edge L4 (right edge) of the chip in the X direction.In a region where the address terminal 21 and command terminal 22 areplaced, which region is included in the peripheral circuit region PE0,circuit blocks related to the address signal ADD and command signal COMare also placed. For example, the address control circuit 32, commanddecoder 34, etc., are placed in that region.

The data input/output terminal DQ processes data of 16 bits. A datainput/output terminal LDQ (=each of input/output terminals DQ0 to DQ7)that processes data of 8 bits comprising one half of the data of 16 bitsis disposed on a part dose to the central area of the chip, and a datainput/output terminal UDQ (=each of input/output terminals DQ8 to DQ15)that processes data of 8 bits comprising the other half of the 16 bitsof data is disposed on a part close to the edge L4 of the chip.

As shown in FIG. 2, out of four memory cell array regions making up eachmemory bank, two memory cell array regions are assigned to theinput/output terminal LDQ and the other two memory cell array regionsare assigned to the input/output terminal UDQ. The memory cell arrayregions assigned to the input/output terminal LDQ are disposed closer tothe edge L3 (left edge) of the chip, while the memory cell array regionsassigned to the input/output terminal UDQ are disposed closer to theedge L4 (right edge) of the chip.

A region formed between the two memory cell regions assigned to theinput/output terminal LDQ is provided as a peripheral circuit regionPE1, and a region formed between the two memory cell regions assigned tothe input/output terminal UDQ is provided as a peripheral circuit regionPE2. In the peripheral circuit regions PE1 and PE2, data buses DB0L andDB1L and DB0U and DB1U extending in the Y direction are placed.respectively.

The data buses DB0L and DB0U are assigned to the memory banks BANK0 andBANK1 near the edge L1 of the chip and to the memory banks BANK6 andBANK7 near the edge L2 of the chip, and are coupled respectively to thedata buses DB1L and DB1U via buffers BF1. The data buses DB1L and DB1Uare assigned to the memory banks BANK2 to BANK5 near the center of thechip, and are coupled respectively to data buses DB2L and DB2U placed inthe peripheral circuit region PE0, via buffers BF2.

The peripheral circuit region PE0 is provided with the data buses DB2L,DB2U, and DB3L extending in the X direction. The data bus DB2L iscoupled to the data bus DB3L via a buffer BF3. The data bus DB3L iscoupled to the data input/output terminal LDQ. The data bus DB2U iscoupled to the data input/output terminal UDQ.

In this configuration, one half of read data from the memory banksBANK0, BANK1, BANK6, and BANK7 is transferred to the data input/outputterminal LDQ via the data buses DB0L, DB1L, DB2L, and DB3L, while theother half of the read data is transferred to the data input/outputterminal UDQ via the data buses DB0U, DB1U, and DB2U. In this case, onehalf of the read data is transferred to the data input/output terminalLDQ via three buffers BF1 to BF3, while the other half of the read datais transferred to the data input/output terminal UDQ via two buffers BF1and BF2.

One half of read data from the memory banks BANK2 to BANK5 istransferred to the data input/output terminal LDQ via the data busesDB1L, DB2L, and DB3L, while the other half of the read data istransferred to the data input/output terminal UDQ via the data busesDB1U and DB2U. In this case, one half of the read data is transferred tothe data input/output terminal LDQ via two buffers BF2 and BF3, whilethe other half of the read data is transferred to the data input/outputterminal UDQ via one buffer BF2.

The semiconductor device 10 according to this embodiment is a DRAM thatperforms 8-bit pre-fetching, and is therefore capable of reading readdata of up to 128 bits (=8 bits×16 input/output terminals DQ0 to DQ15)for one access. One half and the other half of the read data of 128 bitsread, i.e., one block of data of 64 bits and the other block of data of64 bits, are transferred to the data input/output terminals LDQ and UDQ,respectively, Each data bus DB, therefore, handles data of 64 bits.

In this configuration, however, crosstalk between different lines mustbe prevented. As shown in FIG. 3, therefore, a shielding power line isdisposed on both sides of each of 64 data lines including each data busDB. FIG. 3 depicts the case of the data bus DB0L, in which the data busDB0L is composed of 64 data lines DB0L<0> to DB0L<63> and each of themis shielded on its both sides with a VSS line and a VPERI line. Eachdata bus DB having such a configuration thus needs 129 lines (data linesplus power lines) in total.

FIG. 4 is a timing chart for explaining the operation timing of thesemiconductor device 10 having a prototype-based layout, including FIG.4(A) depicting the transfer of read data from the memory bank BANK0 andFIG. 4(B) depicting the transfer of read data from the memory bankBANK2.

As shown in FIG. 4(A), out of read data from the memory bank BANK0, ablock of read data assigned to the data input/output terminal LDQ istransferred through the data buses DB0L, DB1L, DB2L, and DB3L. In thiscase, a time that the read data takes from the issue of a read commandRD to the read data's arrival at the data input/output terminal LDQ istpd1. Out of the read data from the memory bank BANK0, a block of readdata assigned to the data input/output terminal UDQ is transferredthrough the data buses DB0U, DB1U, and DB2U. In this case, a time thatthe read data takes from the issue of the read command RD to the readdata's arrival at the data input/output terminal UDQ is tpd2 (<tpd1).

As shown in FIG. 4(B), out of read data from the memory bank BANK2, ablock of read data assigned to the data input/output terminal LDQ istransferred through the data buses DB1L, DB2L, and DB3L. In this case, atime that the read data takes from the issue of the read command RD tothe read data's arrival at the data input/output terminal LDQ is tpd3(approximately equal to tpd2). Out of the read data from the memory bankBANK2, a block of read data assigned to the data input/output terminalUDQ is transferred through the data buses DB1U and DB2U. In this case, atime that the read data takes from the issue of the read command RD tothe read data's arrival at the data input/output terminal UDQ is tpd4(<tpd3).

In this manner, according to the prototype-based layout, a time at whichread data from each memory bank arrives at the data input/outputterminal LDQ does not match a time at which the read data arrives at thedata input/output terminal UDQ. In addition, such timing of data arrivalvaries depending on the location of a memory bank to be accessed. Thesefacts apply also to the case of a write operation.

The prototype-based layout, therefore, requires designing that matchestiming of data arrival through other access paths to timing of dataarrival through the access path with the maximum delay (e.g., the pathleading from the memory bank BANK0 to the data input/output terminalLDQ). This puts a limit on access speed.

The prototype-based layout also requires that the data bus DB2L shouldpass through the region in which the address control circuit 32, thecommand decoder 34, etc., are placed. The data bus DB2L is a line havingnothing to do with the operation of the address control circuit 32 andthe command decoder 34 and yet must pass through the region includingthe address control circuit 32 and command decoder 34. This leads to aproblem that a region for forming lines necessary for the operation ofthe address control circuit 32 and command decoder 34 is reduced andconsequently a degree of freedom in line layout decreases.

Layouts of the semiconductor device 10 according to first and secondembodiments will then be described.

FIG. 5 is a plan view of a layout of the semiconductor device 10according to a first embodiment.

In the first embodiment, the same square semiconductor chip as theprototype of the semiconductor device 10 is used, which chip has theedges L1 and L2 extending in the X direction and the edges L3 and L4extending in the Y direction. According to the first embodiment of thepresent invention, however, the memory cell arrays 11 comprise 8 memorybanks divided into 16 memory cell array regions ARY0 to ARY15 arrangedinto 2 columns of memory cell array regions in the X direction and into8 rows of memory cell array regions in the Y direction. Each row of 2memory cell array regions comprises one memory bank. The memory cellarray regions arranged closer to one edge L3 (left edge) of the chip inthe X direction are assigned to the data input/output terminal LDQ,while the memory cell array regions arranged closer to the other edge L4(right edge) of the chip in the X direction are assigned to the datainput/output terminal UDQ.

The memory cell array regions ARY0 to ARY7 comprise the memory banksBANK0 to BANK3 are arranged closer to one edge L1 (upper edge) of thechip in the Y direction, while the memory cell array regions ARY8 toARY15 making up the memory banks BANK4 to BANK7 are arranged closer tothe other edge L2 (lower edge) of the chip in the Y direction.

More specifically, when the coordinates of the chip in the X directionand the Y direction are divided into coordinates X1 to X3 andcoordinates Y1 to Y3, respectively, the memory cell, array regions ARY0,ARY2, ARY4, and ARY6 are arranged in increasing order in the Y directionin a region where the coordinates X2 and Y2 intersect. In the samemanner, the memory cell array regions ARY1, ARY3, ARY5, and ARY7 arearranged in increasing order in the Y direction in a region where thecoordinates X3 and Y2 intersect, the memory cell array regions ARY8,ARY10, ARY12, and ARY14 are arranged in increasing order in the Ydirection in a region where the coordinates X2 and Y3 intersect, and thememory cell array regions ARY9, ARY11, ARY13, and ARY15 are arranged inincreasing order in the Y direction in a region where the coordinates X3and Y3 intersect.

The region corresponding to the chip coordinates X1 and Y1 is aperipheral circuit region, which include a peripheral circuit regionPE10 representing a region where the coordinates X1 and Y1 intersect, aperipheral circuit region PE11 representing a region where thecoordinates X1 and Y2 intersect, a peripheral circuit region PE12representing a region where the coordinates X1 and Y3 intersect, aperipheral circuit region PE13 representing a region where thecoordinates X2 and Y1 intersect, and a peripheral circuit region PE14representing a region where the coordinates X3 and Y1 intersect. Theperipheral circuit region PE10 is the central region located at thecenter of the chip.

The address terminal 21, the command terminal 22, and circuit blocksrelated to those terminals, such as the address control circuit 32 andthe command decoder 34, are placed in the peripheral circuit regionPE13. The data input/output terminal DQ and circuit blocks relatedthereto, such as the data input/output circuit 39, are placed in theperipheral circuit region PE14. The data input/output terminal DQprocesses data of 16 bits. The data input/output terminal LDQ (=each ofinput/output terminals DQ0 to DQ7) that processes data of 8 bitscomprising one half of the data of 16 bits is disposed on a part closeto the central region of the chip, and the data input/output terminalUDQ (=each of input/output terminals DQ8 to DQ15) that processes data,of 8 bits comprising the other half of the 16 bits of data is disposedon a part close to the edge L4 of the chip.

The peripheral circuit region PE11 includes the data buses DBcorresponding to the memory banks BANK0 to BANK3 and extending in the Ydirection and with other circuit blocks (fuse circuit 40, etc.).Similarly, the peripheral circuit region PE12 includes the data buses DBcorresponding to the memory banks BANK4 to BANK7 and extending in the Ydirection and with other circuit blocks (fuse circuit 40, etc.).

More specifically, the data buses DB are arranged in the followingmanner. The data buses DB0L and DB0U assigned to the memory banks BANK0and BANK1 and the data buses DB1L and DB1U assigned to the memory banksBANK2 and BANK3 are placed in the peripheral circuit region PE11. Thedata bus DB0L is coupled to the data bus DB1L via the buffer BF1L, andthe data bus DB0U is coupled to the data bus DB1U via the buffer BF1U.

Similarly, the data buses DB0L, and DB0U assigned to the memory banksBANK6 and BANK7 and the data buses DB1L and DB1U assigned to the memorybanks BANK4 and BANK5 are placed in the peripheral circuit region PE12.The data bus DB0L is coupled to the data bus DB1L via the buffer BF1L,and the data bus DB0U is coupled to the data bus DB1U via the bufferBF1U.

The data buses DB1L are coupled to the data bus DB2L via the buffersBF2L. Similarly, the data buses DB1U are coupled to the data bus DB2Uvia the buffers The data bus DB2L has a portion extending in the Ydirection to couple together the upper and lower buffers BF2L, and aportion extending in the X direction from a connection point N1 locatedin the central region of the chip. Similarly, the data bus DB2U has aportion extending in the Y direction to couple together the upper andlower buffers BF2U, and a portion extending in the X direction from aconnection point N2 located in the central region of the chip.

The data buses DB2L and DB2U extend from the peripheral circuit regionPE10, i.e., central region, to the peripheral circuit region PE14. Thedata bus DB2U is coupled to the data bus DB3U via a buffer BF3U. Thedata bus DB2L is coupled to the data input/output terminal LDQ, and thedata bus DB3U is coupled to the data input/output terminal UDQ.

In this manner, according to the layout of the first embodiment, no databus DB needs to be laid in the peripheral circuit region PE13 in whichthe address control circuit 32, the command decoder 34, etc., areplaced. Therefore, the region for forming lines necessary for theoperation of the address control circuit 32 and command decoder 34,which region is reduced in the prototype-based layout of FIG. 2, is notreduced in the layout of the first embodiment.

The semiconductor device 10 according to this embodiment is a DRAM thatperforms 8-bit pre-fetching, and is therefore capable of reading readdata of up to 128 bits (=8 bits×16 input/output terminals DQ0 to DQ15)for one access. One half and the other half of the read data of 128 bitsread, i.e., one block of data of 64 bits and the other block of data of64 bits, are transferred to the data input/output terminals LDQ and UDQ,respectively, Each data bus DB, therefore, handles data of 64 bits.

However, as described above referring to FIG. 3, to prevent crosstalkbetween different lines, both sides of each of 64 data lines comprisingeach data bus DB must be shielded with respective shielding power lines.Each data bus DB thus needs 129 lines (data lines plus power lines) intotal.

The semiconductor device 10 of this embodiment has a first operationmode and a second operation mode.

The first operation mode is a mode in which both data input/outputterminals LDQ and UDQ are used. When the first operation mode isselected, data of 16 bits is input/output via the data input/outputterminals LDQ and UDQ. In this case, data of 128 bits (=8 bits×16input/output terminals DQO to DQ15) is input/output to/from the memorycell arrays 11 for one access.

The second operation mode is a mode in which the data input/outputterminal LDQ is used and the data input/output terminal UDQ is not used.When the second operation mode is selected, the data input/outputterminal LDQ is not used and data of 8 bits is input/output via the datainput/output terminal LDQ. In this case, data of 64 bits (=8 bits×8input/output terminals DQ0 to DQ7) is input/output to/from the, memorycell arrays 11 for one access.

When the first operation mode is selected, one half of read data fromthe memory banks BANK0, BANK1, BANK6, and BANK7 is transferred to thedata input/output terminal LDQ via the data buses DB0L, DB1L, and DB2L,while the other half of the read data is transferred to the datainput/output terminal UDQ via the data buses DB0U, DB1U, DB2U, and DB3U.In this case, one half of the read data is transferred to the datainput/output terminal LDQ via two buffers BF1L and BF2L, while the otherhalf of the read data is transferred to the data input/output terminalUDQ via three buffers BF1U to BF3U.

One half of read data from the memory banks BANK2 to BANK5 istransferred to the data input/output terminal LDQ via the data busesDB1L and DB2L, while the other half of the read data is transferred tothe data input/output terminal UDQ via the data buses DB1U, DB2U, andDB3U. In this case, one half of the read data is transferred to the datainput/output terminal LDQ via one buffer BF2L, while the other half ofthe read data is transferred to the data input/output terminal UDQ viatwo buffers BF2U and BF3U.

When the second operation mode is selected, two memory cell arrayregions comprising each memory bank function as two memory banksdifferent from each other. When the second operation mode is selected,therefore, the semiconductor device 10 of this embodiment is configuredto include 16 memory banks BANK0 to BANK15, which are assigned in such amanner as shown in FIG. 6.

When the second operation mode is selected, the data buses DB1U arecoupled to the data bus DB2L via buffers BF4. The buffer BF4 is a bufferthat is activated when the second operation mode is selected. When thefirst operation mode is selected, the buffer BF4 is deactivated to ahigh-impedance-carrying state.

In this configuration, read data from the memory banks BANK0, BANK1,BANK4, and BANK5 is transferred to the data input/output terminal, LDQvia the data buses DB0L, DB1L, and DB2L, while read data from the memorybanks BANK2, BANK3, BANK6, and BANK7 is transferred to the datainput/output terminal LDQ via the data buses DB0U, DB1U, and DB2L.

Read data from the memory banks BANK8, BANK9, BANK12, and BANK13 istransferred to the data input/output terminal LDQ via the data busesDB1L and DB2L, while read data read out of the memory banks BANK10,BANK11, BANK14, and BANK15 is transferred to the data input/outputterminal LDQ via the data buses DB1U and DB2L.

FIG. 7 is a plan view for explaining a configuration of one memory cellarray ARY.

As shown in FIG. 7, the memory cell array region ARY includes memorycell array subregions ARYa and ARYb divided in the Y direction by therow decoder 12. On one ends in the X direction of the memory cell arraysubregions ARYa and ARYb, the column decoders 13 and the main amplifiersMAMP are disposed. The main amplifier MAMP assigned to the memory cellarray subregion ARYa includes unit amplifiers MA0 to MA31 for processingdata of 31 bits, and the main amplifier MAMP assigned to the memory cellarray subregion ARYb includes unit amplifiers MA32 to MA63 forprocessing data of 31 bits.

The unit amplifiers MA0 to MA63 are coupled to main IO lines MIOT/MIOB0to MIOT/MIOB63 extending in the X direction, respectively. Each main IOline MIOT/MIOB is coupled to each local IO line LIOT/LIOB extending inthe Y direction, via a switch circuit TG. The local IO line LIOT/LIOB iscoupled to the sense amplifier SAMP via a column switch YSW. Theoperation of the column switch YSW is controlled by a column selectionsignal YS supplied from the column decoder 34.

FIG. 8 is a circuit diagram of the buffer BF1L.

As shown in FIG. 8, the buffer BF1L is a TRI-STATE buffer controlled byan enable signal EN that is activated upon execution of the readoperation. When the enable signal EN is activated to a high-voltagelevel, read data on the data bus DB0L is transferred through the bufferBF1L to the data bus DB1L. When the enable signal EN is deactivated to alow-voltage level, on the other hand, the output node of the buffer BF1Lshifts to a high-impedance-carrying state.

FIG. 8 depicts the buffer BF1L used upon execution of the readoperation. The circuit configuration of the buffer BF1L used uponexecution of the write operation is the same as the circuitconfiguration of the buffer BF1L of FIG. 8, except that the input andoutput nodes of the former buffer are reverse in position to the same ofthe latter buffer. The buffer BF1U also has the same circuitconfiguration as that of the buffer BF1L of FIG. 8.

FIG. 9 is a circuit diagram of a combination of buffers BF2L, BF2U, andBF4.

As shown in FIG. 9, the buffers BF2L, BF2U, and BF4 are all TRI-STATEbuffers. In addition to the enable signal EN, a mode signal MODE and alower bank signal BANKL are used also to control the buffers BF2L, BF2U,and BF4. The mode signal MODE goes high when the first operation mode(in which both data input/output terminals LDQ and UDQ are used) isselected, and goes low when the second operation mode (in which only thedata input/output terminal LDQ is used) is selected. The lower banksignal BANKL goes high when the banks BANK0, BANK1, BANK4, BANK5, BANK8,BANK9, BANK12, and BANK13 arranged on the left side in the chip areselected in the second operation mode, and goes low when the banksBANK2, BANK3, BANK6, BANK7, BANK10, BANK11, BANK14, and BANK15 arrangedon the right side in the chip are selected in the second operation mode.

In the configuration of FIG. 9, when the first operation mode isselected, activating the enable signal EN to a high-voltage level putsboth buffers BF2L and BF2U into an activated state. As a result, readdata on the data bus DB1L and read data on the DB1U are transferred tothe data buses DB2L and DB2U, respectively. In this case, the buffer BF4is kept in a high-impedance-carrying state, regardless of the enablesignal EN being at a high-voltage level or a low-voltage level.

When the second operation mode is selected, activating the enable signalEN to a high-voltage level puts one of the buffers BF2L and BF4 into anactivated state, based on the lower bank signal BANKL. As a result, readdata on the data bus DB1L or DB1U is transferred to the data bus DB2L.In this case, the buffer BF2U is kept in a high-impedance-carryingstate, regardless of the enable signal EN being at a high-voltage levelor a low-voltage level.

FIG. 10 is a timing chart for explaining, operation timing according tothe first embodiment, including FIG. 10(A) depicting transfer of readdata from the memory bank BANK0 in the first operation mode and FIG.10(B) depicting transfer of read data from the memory bank BANK2 in thefirst operation mode.

As shown in FIG. 10(A), out of read data from the memory bank BANK0, ablock of read data assigned to the data input/output terminal LDQ istransferred via the data buses DB0L, DB1L, and DB2L. In this case, atime that the read data takes from the issue of the read command RD tothe read data's arrival at the data input/output terminal LDQ is tpd11.Out of the read data from the memory bank BANK0, a block of read dataassigned to the data input/output terminal UDQ is transferred via thedata buses DB0U, DB1U, DB2U, and DB3U. In this case, a time that theread data takes from the issue of the read command RD to the read data'sarrival at the data input/output terminal UDQ is tpd12 (>tpd11).

As shown in FIG. 10(B), out of read data from the memory bank BANK2, ablock of read data assigned to the data input/output terminal LDQ istransferred via the data buses DB1L and DB2L. In this case, a time thatthe read data takes from the issue of the read command RD to the readdata's arrival at the data input/output terminal LDQ is tpd13 (<tpd11).Out of the read data from the memory bank BANK2, a block of read dataassigned to the data input/output terminal UDQ is transferred via thedata buses DB1U, DB2U, and DB3U. In this case, a time that the read datatakes from the issue of the read command RD to the read data's arrivalat the data input/output terminal UDQ is tpd14 (approximately equal totpd11).

FIG. 11 is a plan view of a layout of the semiconductor device 10according to a second embodiment, showing a case where the firstoperation mode is selected.

As shown in FIG. 11, the layout according to the second embodiment ofthe present invention and the layout according to the first embodimentof FIG. 5 are the same in the basic positional relationship between thememory cell array regions ARY and the peripheral circuit region PE butare different in the locations of assignment of the memory banks and inthe configuration of the data buses DB.

Assignment of the memory banks will first be described. When thelocations of the memory cell array regions ARY0 to ARY15 are the same asthe locations of the memory cell array regions ARY0 to ARY15 shown inFIG. 5, each memory bank BANKi (i=0 to 7) in FIG. 11 comprises a memorycell array region ARYi and a memory cell array region ARYi+8. Forexample, the memory bank BANK0 comprises the memory cell array regionARY0 and the memory cell array region ARY8.

As a result, two memory cell array regions comprising the same memorybank are always different in their coordinates in the Y direction and intheir distances in the Y direction to the peripheral circuit region PE13or PE14. For example, for the case of the memory cell array regions ARY0and ARY8 comprising the memory bank BANK0, the distance from the memorycell array region ARY0 to the peripheral circuit region PE13 is greaterthan the distance from the memory cell array region ARY8 to theperipheral circuit region PE13.

The details of the arrangement of the data buses DB are as follows. Inthe peripheral circuit region PE11, data buses DB0La, DB0Ub, and DB1Laare placed such that the data bus DB0La is assigned to the memory cellarray regions ARY0 and ARY2, the data bus DB0Ub is assigned to thememory cell array regions ARY4 and ARY6, and the data bus DB1La iscoupled to the data bus DB0La via a buffer BF1La. Data buses DB0Lc,DB0LUd, and DB1Lc and a buffer BF1Lc identical in configuration with thedata buses DB0La, DB0Ub, and DB1La and the Buffer BF1La are alsoprovided for the memory cell array regions ARY1, ARY3, ARY5, and ARY7.

Likewise, in the peripheral circuit region PE12, data buses DB0Lb,DB0Ua, and DB1Lb are placed such that the data bus DB0Lb is assigned tothe memory cell array regions ARY12 and ARY14, the data bus DB0Ua isassigned to the memory cell array regions ARY8 and ARY10, and the databus DB1Lb is coupled to the data bus DB0Lb via a buffer BF1Lb. Databuses DB0Ld, DB0Uc, and DB1Ld and a buffer BF1Ld identical inconfiguration with the data buses DB0Lb, DB0Ua, and DB1Lb and the BufferBF1Lb are also provided for the memory cell array regions ARY9, ARY11,ARY13, and ARY15.

The data buses DB1La to DB1Ld are coupled to the data bus DB2L viabuffers BF2La to BF2Ld, respectively. The data buses DB1Ua DB1Ud arecoupled to the data bus DB1U via buffers BF1U to BF1Ud, respectively.The data bus DB2L has a portion extending in the Y direction to coupletogether the buffers BF2La to BF2Ld, and a portion extending in the Xdirection from the connection point N2 located in the central region ofthe chip. Similarly, the data bus DB1U has a portion extending in the Ydirection to couple together the buffers BF1Ua to BF1Ud, and a portionextending in the X direction from the connection point N1 located in thecentral region of the chip.

The data buses DB2L and DB1U extend from the peripheral circuit regionPE10, i.e., central region, to the peripheral circuit region PE14. Thedata bus DB1U is coupled to the data bus DB2U via the buffer BF3U. Thedata bus DB2L is coupled to the data input/output terminal LDQ, and thedata bus DB2U is coupled to the data input/output terminal UDQ.

When the first operation mode is selected in the layout of thisembodiment, transmission paths for read data read out of the memorybanks are taken as follows.

One half of read data from the memory banks BANK0 and BANK1 istransferred to the data input/output terminal LDQ via the data busesDB0La, DB1La, and DB2L, while the other half of the read data istransferred to the data input/output terminal UDQ via the data busesDB0Ua, DB1U, and DB2U. In this case, one half of the read data istransferred to the data input/output terminal LDQ via two buffers BF1Laand BF2La, while the other half of the read data is transferred to thedata input/output terminal UDQ via two buffers BF1UA and BF3U.

The transmission path comprises the data buses DB0La, DB1La, and DB2Lcan be divided into a section extending from the memory cell arrayregions ARY0 and ARY2 to the connection point N2 and a section extendingfrom the connection point N2 to the data input/output terminal LDQ. Theformer section can be further divided into a subsection extending fromthe memory cell array regions ARY0 and ARY2 to the buffer BF1La and asubsection extending from the buffer BF1La to the connection point N2.The transmission path comprising the data buses DB0Ua, DB1U, and DB2Ucan be divided into a section extending from the memory cell arrayregions ARY8 and ARY10 to the connection point N1 and a sectionextending from the connection point N1 to the data input/output terminalUDQ.

One half of read data from the memory banks BANK2 and BANK3 istransferred to the data input/output terminal LDQ via the data busesDB0Lc, DB1Lc, and DB2L, while the other half of the read data istransferred to the data input/output terminal UDQ via the data busesDB0Uc, DB1U, and DB2U. In this case, one half of the read data istransferred to the data input/output terminal LDQ via two buffers BF1Lcand BF2Lc, while the other half of the read data is transferred to thedata input/output terminal UDQ via two buffers BF1Uc and BF3U.

The transmission path comprising the data buses DB0Lc, DB1Lc, and DB2Lcan be divided into a section extending from the memory cell arrayregions ARY1 and ARY3 to the connection point N2 and a section extendingfrom the connection point N2 to the data input/output terminal LDQ. Theformer section can be further divided into a subsection extending fromthe memory cell array regions ARY1 and ARY3 to the buffer BF1Lc and asubsection extending from the buffer BF1Lc to the connection point N2.The transmission path comprising the data buses DB0Uc, DB1U, and DB2Ucan be divided into a section extending from the memory cell arrayregions ARY9 and ARY11 to the connection point N1 and a sectionextending from the connection point N1 to the data input/output terminalUDQ.

One half of read data from the memory banks BANK4 and BANK5 istransferred to the data input/output terminal LDQ via the data busesDB0Lb, DB1Lb, and DB2L, while the other half of the read data istransferred to the data input/output terminal UDQ via the data busesDB0Ub, DB1U, and DB2U. In this case, one half of the read data istransferred to the data input/output terminal LDQ via two buffers BF1Lband BF2Lb, while the other half of the read data is transferred to thedata input/output terminal UDQ via two buffers BF1Ub and BF3U.

The transmission path comprising the data buses DB0Lb, DB1Lb, and DB2Lcan be divided into a section extending from the memory cell arrayregions ARY12 and ARY14 to the connection point N2 and a sectionextending from the connection point N2 to the data input/output terminalLDQ. The former section can be further divided into a subsectionextending from the memory cell array regions ARY12 and ARY14 to thebuffer BF1Lb and a subsection extending from the buffer BF1Lb to theconnection point N2. The transmission path comprising the data busesDB0Ub, DB1U, and DB2U can be divided into a section extending from thememory cell array regions ARY4 and ARY6 to the connection point N1 and asection extending from the connection point N1 to the data input/outputterminal UDQ.

One half of read data from the memory banks BANK6 and BANK7 istransferred to the data input/output terminal LDQ via the data busesDB0Ld, DB1Ld, and DB2L, while the other half of the read data istransferred to the data input/output terminal UDQ via the data busesDB0Ud, DB1U, and DB2U. In this case, one half of the read data istransferred to the data input/output terminal LDQ via two buffers BF1Ldand BF2Ld, while the other half of the read data is transferred to thedata input/output terminal UDQ via two buffers BF1Ud and BF3U.

The transmission path comprising the data buses DB0Ld, DB1Ld, and DB2Lcan be divided into a section extending from the memory cell arrayregions ARY13 and ARY15 to the connection point N2 and a sectionextending from the connection point N2 to the data input/output terminalLDQ. The former section can be further divided into a subsectionextending from the memory cell array regions ARY13 and ARY15 to thebuffer BF1Ld and a subsection extending from the buffer BF1Ld to theconnection point N2. The transmission path comprising the data busesDB0Ud, DB1U, and DB2U can be divided into a section extending from thememory cell array regions ARY5 and ARY7 to the connection point N1 and asection extending from the connection point N1 to the data input/outputterminal UDQ.

When the second operation mode is selected, the memory banks BANK0 toBANK15 are assigned according to this embodiment in such a manner asshown in FIG. 12.

When the second operation mode is selected, the data buses DB0Ua toDB0Ud are coupled to the data buses DB1La to DB1Ld via buffers BF4a toBF4d, respectively. The buffers BF4a to BF4d are buffers that areactivated when the second operation mode is selected. When the firstoperation mode is selected, therefore, the buffers BF4a to BF4d shiftsto a high-impedance-carrying state.

In this configuration, read data from the memory banks BANK0 to BANK7 istransferred to the data input/output terminal LDQ via the data busesDB0La to DB0Ld, DB1La to DB1Ld, and DB2L, while read data read out ofthe memory banks BANK8 to BANK15 is transferred to the data input/outputterminal LDQ via the data buses DB0Ua to DB0Ud, DB1La to DB1Ld, andDB2L.

FIG. 13 is a diagram for explaining the structure of the data bus DB,including FIG. 13(A) depicting the structure of the data bus DB0La, FIG.13(B) depicting the structures of the data buses DB0Ub and DB1La, FIG.13(C) depicting the structures of the data buses DB1U and DB2L, and FIG.13(D) depicting the structure of the data bus DB2U.

As shown in FIG. 13(A), both sides of each of 64 data lines comprisingthe data bus DB0La is shielded with respective shielding power lines VSSand VPERI. Hence a region for forming the data bus DB0La needs toinclude 129 lines in total. This fact applies also to other data busesDB0Lb to DB0Ld.

As shown in FIG. 13(B), 64 data lines comprising the data bus DB0Ub and64 data lines comprising the data bus DB1La are arranged alternately,and the shielding power lines VSS and VPERI are disposed respectively onboth sides of a group of 128 data lines comprising the data buses DB0Uband DB1La. Hence a region for forming the data buses DB0Ub and DB1Laneeds to include 130 lines in total. In this configuration, the databuses DB0Ub and DB1La function as shields to give protection each other.This fact applies also to other combinations of data buses, that is,combinations of the data buses DB0Ua and DB1Lb, DB0Ud and DB1Lc, andDB0Uc and DB1Ld.

As shown in FIG. 13(C), 64 data lines comprising the data bus DB1U and64 data lines comprising the data bus DB2L are arranged alternately, andthe shielding power lines VSS and VPERI are disposed respectively onboth sides of a group of 128 data lines making up the data buses DB1Uand DB2L. Hence a region for forming the data buses DB1U and DB2L needsto include 130 lines in total. In this manner, the data buses DB1U andDB2L also function as shields to give protection each other.

As shown in FIG. 13(D), both sides of each of 64 data lines comprisingthe data bus DB2U is shielded with respective shielding power lines VSSand VPERI. Hence a region for forming the data bus DB2U needs to include129 lines in total.

In this manner, according to the layout of this embodiment, one part andthe other part of the data bus DB function as shields to give protectioneach other. As a result, the number of power lines needed as shields canbe reduced.

FIG. 14 is a first timing chart for explaining operation timingaccording to the second embodiment. FIG. 14 depicts transfer of readdata from the memory bank BANK0 in the first operation mode. Operationtiming in cases of transferring read data from the memory banks BANK1 toBANK7 is basically the same as the operation timing depicted in thefirst timing chart of FIG. 14.

As shown in FIG. 14, out of read data from the memory bank BANK0responsive to the read command RD, a block of read data assigned to thedata input/output terminal LDQ (a block of read data stored in thememory cell array region ARY0) is transferred via the data buses DB0La,DB1La, and DB2L. In this case, the read data passes through two buffersand a time that the read data takes from the issue of the read commandRD to the read data's arrival at the data input/output terminal LDQ istpd21.

Out of the read data from the memory bank BANK0, a block of read dataassigned to the data input/output terminal UDQ (a block of read datastored in the memory cell array region ARY8) is transferred via the databuses DB0Ua, DB1U, and DB2U. In this case, the read data passes throughtwo buffers and a time that the read data takes from the issue of theread command RD to the read data's arrival at the data input/outputterminal UDQ is tpd22.

The data bus DB assigned to the data input/output terminal LDQ and thedata bus DB assigned to the data input/output terminal UDQ are almostequal in total line length with each other and carry buffers equal innumber with each other. Specifically, the data bus DB assigned to thedata input/output terminal LDQ has a section 1 extending from the memorycell array region ARY0 to the connection point N2 and, a section 2extending from the connection point N2 to the data input/output terminalLDQ, while the data bus DB assigned to the data input/output terminalUDQ has a section 3 extending from the memory cell array region ARY8 tothe connection point N1 and a section 4 extending from the connectionpoint N1 to the data input/output terminal UDQ. When the lengths of thesections 1 to 4 are denoted as S1 to S4, respectively, the followingrelations are satisfied.

S1>S3

S2<S4

S1+S2 is approximately equal to S3+S4

Since both of the data assigned to the data input/output terminal LDQand the data assigned to the data input/output terminal UDQ pass throughtwo buffers, respectively, the arrival time tpd21 roughly matches thearrival time tpd22. This allows faster data transfer.

When read data is transferred via the data bus DB1La, the data busDB0Ub, i.e., the data lines comprising the data bus DB0Ub that arearranged alternately with the data lines comprising the data bus DB1La,functions as a shield. In the same manner, when read data is transferredvia the data bus DB0Ua, the data bus DB1Lb, i.e., the data linescomprising the data bus DB1Lb that are arranged alternately with thedata lines comprising the data bus DB0Ua, function as a shield.

Obviously, data is also transferred via the data buses DB0Ub and DB1Lbfunctioning as shields. However, these data buses DB0Ub and DB1Lb areassigned to the memory banks BANK4 and BANK5 different from the memorybank BANK0. Therefore, simultaneous data transfer through both databuses functioning as shields to each other does not happen. This meansthat when data is transferred via one data bus DB, the voltage level ofthe other data bus DB is always fixed. This allows both data buses DB toexert their shield effects for mutual protection.

FIG. 15 is a second timing chart for explaining the operation timingaccording to the second embodiment. FIG. 15 depicts transfer of writedata to be written to the memory bank BANK0 in the first operation mode.Operation timing in cases of writing write data to the memory banksBANK1 to BANK7 is basically the same as the operation tinting depictedin the second timing chart of FIG. 15.

As shown in FIG. 15, out of write data input to the data input/outputterminals LDQ and UDQ responsive to a write command WR, a block of writedata input to the data input/output terminal LDQ is transferred to thememory cell array region ARY0 via the data buses DB2L, DB1La, and DB0La,and a block of write data input to the data input/output terminal UDQ istransferred to the memory cell array region ARY8 via the data busesDB2U, DB1U, and DB0Ua.

In this case, a time that the write data takes from its being input tothe data input/output terminal LDQ to its arrival at the memory cellarray region ARY0 is tpd31. A time that the write data takes from itsbeing input to the data input/output terminal UDQ to its arrival at thememory cell array region ARY8 is tpd32 (approximately equal to tpd31).

In this manner, according to this embodiment, a time at which the writedata assigned to the data input/output terminal LDQ arrives at thememory cell array ARY0 roughly matches a time at which the write dataassigned to the data input/output terminal UDQ arrives at the memorycell array ARY8. In addition, in the same manner as in the case of theread operation, the data bus DB0Ub functions as a shield when the writedata is transferred via the data bus DB1La, and the data bus DB1Lbfunctions as a shield when the write data is transferred via the databus DB0Ua.

FIG. 16 is a third timing chart for explaining the operation timingaccording to the second embodiment. FIG. 16 depicts transfer of readdata read out of the memory banks BANK0 and BANK12 in the secondoperation mode. Operation timing in cases of reading read data fromother memory banks is basically the same as the operation timingdepicted in the third timing chart of FIG. 16.

As shown in FIG. 16, read data from the memory bank BANK0 responsive tothe read command RD is transferred to the data input/output terminal LDQvia the data buses DB0La, DB1La, and DB2L. In this case, a time that theread data takes from the issue of the read command RD to the read data'sarrival at the data input/output terminal LDQ is tpd21.

Read data from the memory bank BANK12 responsive to another read commandRD is transferred to the data input/output terminal LDQ via the databuses DB0Ub, DB1La, and DB2U. In this case, a time that the read datatakes from the issue of the read command RD to the read data's arrivalat the data input/output terminal LDQ is tpd23.

The data bus DB assigned to the memory bank BANK0 and the data bus DBassigned to the memory bank BANK12 are almost equal in total line lengthwith each other and carry buffers equal in number with each other. As aresult, the arrival time tpd21 roughly matches the arrival time tpd23.

In this manner in the second operation mode, each access time requiredfor accessing each memory bank is almost the same. This holds true forthe case of the write operation as well as for the case of the readoperation. Because access to a certain memory bank and access to anothermemory bank do not occur simultaneously but always occur at differentpoints in time across a given time interval, one of two data buses DBthat shield each other is always given a fixed potential.

In the example of FIG. 16, when the read data from the memory bank BANK0is transferred via the data bus DB1La, data transfer from the memorybank BANK12 via the data bus DB0Ub is not carried out yet. As a result,a proper shield effect can be achieved. When the read data from thememory bank BANK12 is transferred via the data bus DB0Ub, on the otherhand, data transfer from the memory bank BANK0 via the data bus DB1La isalready finished. A proper shield effect, therefore, can also beachieved in this case.

When the read data from the memory bank BANK12 is transferred via thedata bus DB1La, data transfer from the memory bank BANK12 via the databus DB0Ub is already finished. A proper shield effect, therefore, canalso be achieved in this case.

In this manner, according to the second embodiment of the presentinvention, a shift in data input/output timing between memory banks orbetween memory cell array regions does not arise, regardless of whichoperation mode is selected. Hence high-speed accessing can be realized.In addition, two data buses DB that transfer data in different timingare combined such that data lines comprising one data bus and data linescomprising the other data bus are arranged alternately to offer a shieldeffect. This allows a reduction in the number of power-line-utilizedshields.

According to the second embodiment, a method of assigning memory bankswhen the first operation mode is selected is not limited to the methodof assignment shown in FIG. 11. A method of assignment shown in FIG. 17or 18 may also be used.

According to the method of assignment shown in FIG. 17, for example, twomemory cell array regions ARY comprising the memory bank BANK0 in thefirst operation mode are located in a region where the coordinates X2and coordinates Y2 intersect and a region where the coordinates X3 andcoordinates Y2 intersect, respectively. According to the method ofassignment shown in FIG. 18, for example, two memory cell array regionsARY comprising the memory bank BANK0 in the first operation mode arelocated in the region where the coordinates X2 and coordinates Y2intersect and a region where the coordinates X3 and coordinates Y3intersect, respectively. These methods of assignment achieve the sameeffect as the effect achieved in the second embodiment.

The preferred embodiments of the present invention have been describedabove. The present invention is not limited to the above embodiments butmay be modified into various forms of applications on the condition thatthe modification does not deviate from the substance of the invention.It is obvious that modified forms of applications are also included inthe scope of the invention.

For example, the above embodiments relate to cases where the presentinvention is applied to DRAM. A device to which the invention isapplied, however, is not limned to DRAM. For another example, SRAM(Static Random Access Memory), Flash memory, ReRAM (Resistive RandomAccess Memory) and MRAM (Magneto resistive Random Access Memory) etc.are also applicable to this invention as the device.

What is claimed is:
 1. A device comprising: an active area having asquare shape, the active area being divided into first, second, third,fourth, fifth, sixth, seventh, eighth and ninth regions arranged in amatrix, the first, second, third and fourth regions being arranged atrespective corners of the square, the fifth region being arranged at acenter of the matrix, and the sixth, seventh, eighth and ninth regionsbeing arranged between the first and second regions, the second andthird regions, the third and fourth regions and the fourth and firstregions, respectively; a plurality a memory arrays each including aplurality of memory cells arranged in each of the first, second, thirdand fourth regions; a plurality of data terminals arranged in the eighthregion; a first switching buffer coupled between a data node of one ofthe memory arrays and one of the data terminals, the first switchingbuffer being arranged in the seventh region; and a second switchingbuffer coupled between the data node of the one of the memory cellarrays and a different one of the data terminals, the second switchingbuffer being arranged in the seventh region.
 2. The device of claim 1,wherein the plurality of data terminals are arranged in a firstdirection and the first and second switching buffer are arranged in asecond direction crossing the first direction.
 3. The device of claim 1,wherein a position of the first switching buffer is closer to the fifthregion than the second switching buffer and a position of the differentone of the data terminals is closer to the fifth region that the one ofthe data terminals.
 4. The device of the claim 1, further comprising afirst buffer coupled between an additional data node of an additionalone of the memory arrays and the different one of the data terminals,the first buffer being arranged in the seventh region.
 5. The device ofthe claim 4, wherein the additional data node is electricallydisconnected from the one of the data terminals.
 6. The device of theclaim 1, further comprising a plurality of address terminals arranged inthe sixth region and a plurality of command terminals arranged in thesixth region.
 7. The device of the claim 6, wherein each of the fifthregion and the eighth region is free from an address terminal and acommand terminal arid each of the fifth region and the sixth region isfree from a data terminal.
 8. A device comprising: a first memory array;a second memory array; a plurality of first data terminals and seconddata terminals arranged in the first direction between the first memoryarray and the second memory array; a third memory array arranged suchthat the first memory array is between the third memory array and theplurality of first data terminals and second data terminals; a fourthmemory array arranged such that the second memory array is between thefourth memory array and the plurality of first data terminals and seconddata terminals; and a data bus configured to couple each of the firstmemory array and the second memory array to the first data terminals ina first operation mode, couple each of the first memory array and thesecond memory array to the second data terminals in a second operationmode, and couple to the third memory array and the fourth memory arrayto the second data terminals in each of the first operation mode and thesecond operation mode.
 9. The device of claim 8, wherein each of thefirst memory array, the second memory array, the third memory array andthe fourth memory array is configured not to access the first dataterminals in the second operation mode.
 10. The device of claim 8,wherein the plurality of first data terminals and the plurality ofsecond data terminals are arranged in line in the first direction. 11.The device of claim 8, further comprising: a fifth memory array arrangedadjacently to the first memory array in the first direction; a sixthmemory array arranged adjacently to the second memory array in the firstdirection; a seventh memory array arranged adjacently to the thirdmemory array in the first direction; and an eighth memory array arrangedadjacently to the fourth memory array in the first direction; whereinthe data bus is further configured to couple each of the fifth memoryarray and the sixth memory array to the first data terminals in thefirst operation mode, couple each of the fifth memory array and thesixth memory array to the second data terminals in the second operationmode, and couple to the seventh memory array and the eighth memory arrayto the second data terminals in each of the first operation mode and thesecond operation mode.
 12. The device of claim 11, further comprising aplurality of address and command input terminals arranged between thefifth memory array and the sixth memory array.
 13. A device comprising:a first memory array having a first data node; a second memory arrayhaving a second data node; a first data terminal; a second dataterminal; a first transmission path coupled between the first data nodeand the first data terminal; and a second transmission path coupledbetween the second data node and the second data terminal, wherein adistance between the first data node and the first data terminal isgreater than a distance between the second data node and the first dataterminal and wherein a distance between the second data node and thesecond data terminal is less than a distance between the first data nodeand the second data terminal.
 14. The device of claim 13, wherein thefirst and second data terminals are between the first and second memoryarrays.
 15. The device of claim 13, wherein the first transmission pathhas a first total line length and includes a first plurality ofswitching buffers and the second transmission path has a second totalline length and includes a second plurality of switching buffers,wherein the first total line length is equal to the second total linelength and the first plurality of switching buffers is equal in numbersto the second plurality of switching buffers.
 16. The device of claim13, wherein the first transmission path comprises: a first switchingbuffer; a second switching buffer; a first data bus coupled between thefirst data terminal and the first switching buffer; a second data buscoupled between the first switching buffer and the second switchingbuffer; and a third data bus coupled between the second switching bufferand the first data terminal.
 17. The device of claim 16, wherein thesecond transmission path comprises: a third switching buffer; a fourthswitching buffer; a fourth data bus coupled between the second dataterminal and the third switching buffer; a fifth data bus coupledbetween the third switching buffer and the fourth switching buffer; anda sixth data bus coupled between the fourth switching buffer and thesecond data terminal.
 18. The device of claim 13, wherein the firsttransmission path comprises; a first connection point; a first sectionextending from the first data node to the first connection point; and asecond section extending from the first connection point to the firstdata terminal, and wherein the second transmission path comprises: asecond connection point; a third section extending from the second datanode to the second connection point; and a fourth section extending fromthe second connection point to the second data terminal, wherein alength of the first section is greater than a length of the thirdsection and a length of the fourth section is greater than a length ofthe second section.
 19. The device of claim 18, wherein the first dataterminal and the second data terminal are arranged in a line in a firstdirection, and the second and fourth sections are arranged along thefirst direction.
 20. The device of claim 13, wherein the firsttransmission path comprises: a first connection point; a first sectionextending from the first data node to the first connection point, thefirst section including first and second switching buffers; a secondsection extending from the first connection point to the first dataterminal, and wherein the second transmission path comprises: a secondconnection point; a third section extending from the second data node tothe second connection point, the third section including a thirdswitching buffer; and a fourth section extending from the secondconnection point to the second data terminal, the fourth sectionincluding a fourth switching buffer.